This invention relates generally to systems for handling fuel rods for an atomic fuel reactor, and more particularly to systems for automatically removing fuel rods one at a time from a light water breeder reactor (LWBR) module for transfer and storage in a rod transfer container.
The design of a breeder reactor for a light water system imposes requirements on the fuel elements and support grids relative to reaction characteristics. One of the requirements for breeding is that the core have a high ratio of fuel-to-water, which results in closer fuel rod spacing than in, for example, pressurized water reactor (PWR) designs. In a light water breeder reactor (LWBR) core, the fuel, which is in the form of cylindrically shaped ceramic fuel rods, is placed in a close packed, triangular pitch with rod-to-rod spacing of about 0.060 inch.
The present system for removal of expended fuel rods is designed as an underwater robotic system capable of extracing fuel rods, one at a time, from LWBR fuel modules and depositing them in transfer or storage containers. The system utilizes an on-line microcomputer for positioning removal components, calculating fuel rod location coordinates, and maintaining rod movement and storage location records. The system is designed for remote underwater removal of fuel rods, one at a time from LWBR fuel modules which operates by aligning a grappling device over exposed ends of fuel rods for engagement of the rod. The use of an automated rod removal system rather than a simpler method such as manual pulling of rods from overhead walkways, is advantageous in that it limits and closely monitors rod pull force by obtaining accurate rod pull force data; it minimizes the chance for dropping rods into the water pit by monitoring successful engagement of the rod pull tool on the rod end; it pulls rods out of the module vertically to prevent rod bending or unnecessary scratching of the rod cladding; and it is capable of accurately locating the correct rod in the module through twenty feet of water.